Genetics 1

Question 1

Gene

Answer 1

a heritable factor that consists of a length of DNA and controls the synthesis of one polypeptide chain (a segment of the DNA)

Question 2

Gene locus

Answer 2

the specific and fixed position of a gene along a chromosome/DNA

Question 3

Homologous chromosomes vs sister chromatids

Answer 3

have the same bending pattern but can have different gene alleles
have identical genes, identical DNA copies attached at the centromere

Question 4

Allele, homozygous and heterozygous chromosome

Answer 4

a variation of a single gene that differs from other alleles of the same gene by a few base pairs
dominant and recessive alleles, heterozygous are those with different alleles, homozygous chromosome with only one

Question 5

Single nucleotide polymorphism (SNPs)

Answer 5

alternative allele, differing in just a few base pairs from the original gene and this difference doesn’t affect the structure – the result of base-substitution mutations

Question 6

Highly repetitive sequence (HRS)

Answer 6

at telomeres and the centromere (gets lost in the DNA replication)

Question 7

Genome

Answer 7

the complete DNA of a cell (includes both coding and non-coding regions), genome size expressed as the number of base pairs (in humans 3*10^9, number of genes = 23000)

Question 8

Ploidy

Answer 8

the number of complete sets of chromosomes and their genetic information – a cell can be haploid (n) like gametes or diploid (2n) like somatic cells where n is the number of chromosomes in one set

Question 9

Karyotype

Answer 9

describes the number and appearance of the chromosomes in an eukaryotic cell – members of the same species usually have the same karyotype if there is no mutation

Question 10

Karyogram, karyotyping

Answer 10

micrograph of metaphase chromosomes where they are arranged into homologous pairs beginning with autosomes and ending with gonosomes – used for gender prediction and detection of chromosomal abnormalities
the procedure of obtaining the karyogram

Question 11

Autosomes and gonosomes in humans

Answer 11

44 (22 pairs) autosomes (body chromosomes) and two (XX or XY) gonosomes (sex chromosomes)

Question 12

Meiosis

Answer 12

division of diploid somatic cells in sex glands to produce haploid gametes using the mechanism of reducing the number of chromosomes to half the number found in somatic cells and promote genetic variation

Question 13

Miosis steps

Answer 13

Prophase I (the longest phase of meiosis (90% of time required, lasts for hours or days))
Metaphase I (bivalents line up at the equator – random orientation of each pair increases genetic variability)
Anaphase I (bivalents split, each homologous chromosome goes to opposite pole)
Telophase (two clusters formed, nuclear membrane reforms, chromosomes partly uncoil)
Cytokinesis I (possible brief interphase with no DNA replication)
Prophase II Metaphase II Anaphase II (sister chromatids separated) Telophase II Cytokinesis II – produced four genetically different haploid gametes

Question 14

How does random bivalent orientation increase genetic variability

Answer 14

since each bivalent can orient itself in 2 ways, there are 2^n genetically different gametes that can be produced in each organism where n is the number of bivalents (2^23 in humans)

Question 15

Synopsis

Answer 15

pairing up of not completely condensed homologous chromosomes to exchange genes between their non-sister chromatids (crossing over or recombination) – tetrads (4 chromatids)/bivalents (2 chromosomes) formed

Question 16

Chiasma

Answer 16

the place where non-sister chromatids cross over

Question 17

How does crossing over increase genetic variability

Answer 17

results in the recombination of linked genes or the production of new combinations of linked genes in gametes (otherwise only two different gametes would be produced (n=2))

Question 18

Genetic variation can be increased by:

Answer 18

I| Crossing over
II| Random orientation of bivalents
III| Random fertilization of gametes

Question 19

State, in each phase of both mitosis and meiosis, how many and what type (single or double) of chromosomes are present in a human cell

Answer 19

… (table)

Question 20

Mitosis vs meiosis

Answer 20

mitosis is a means of asexual reproduction and meisosis is used to produce gametes which are used in sexual reproduction – only meiosis has crossing over/synopsis and bivalents (homologous pair recognize each other) – mitosis produces two identical daughter cells (somatic) and meiosis four genetically different gametes – in mitosis homologous pairs are blind to each other while they recognize and pair up in meiosis

Question 21

Linked genes

Answer 21

genes most likely to be inherited together (usually not separated in crossing over because of their closeness – otherwise DNA would entangle and mutation would occur)

Question 22

Nondisjunction

Answer 22

when bivalent (homologous chromosomes)/sister chromatids don’t separate during anaphase I/II and it leads to aneuploidy (mutated gametes)

Question 23

Risk factors for nondisjunction

Answer 23

when a parent (especially the mother) is older – the longer the homologous chromosomes are joined (frozen in bivalents in eggs), the more difficult it is to separate them – if an older egg gets fertilized, the probability of it being mutated is greater

Question 24

Chromosomal mutations, and types

Answer 24

changes in structure/number of chromosomes – chromosomal aberration, aneuploidy, and polyploidy – a human can only survive a chromosomal mutation on the 13th, 18th, 21st, and sex chromosome pairs

Question 25

Chromosomal aberration

Answer 25

e.g. cri-du-chat syndrome – one arm on the fifth chromosome missing

Question 26

Aneuploidy

Answer 26

when one pair of a chromosome has a chromosome surplus or missing so the number of chromosomes in a gamete is n+1 or n-1 instead of n, e.g. trisomy (three chromosomes in one pair – most common in gonosomes) like the Down syndrome (trisomy 21) and Klinefelter syndrome (XXY syndrome)

Question 27

Polyploidy

Answer 27

when each homologous pair has an extra chromosome so a gamete has 3n, 4n…number of chromosomes, e.g. triploidy (all pairs have three chromosomes)

Question 28

DNA mutations, and types

Answer 28

permanent structural changes to the DNA of a gene that can be inherited – addition, deletion, substitution (doesn’t have to be detrimental because of degeneration property of the genetic code), translocation, and inversion

Question 29

Types of mutations by how they affect the amino acid produced from the gene

Answer 29

same-sense mutations don’t change the amino acid, non-sense mutations code for a stop codon instead of an amino acid, and mid-sense mutations result in a codon that codes for a different amino acid

Question 30

Sickle-cell anemia

Answer 30

an example of substitution mutation from GTG to GAG which results in glutamic acid being coded for instead of valine which results in a mutated Hb (hemoglobin) with a different secondary and tertiary structure and therefore function – it can carry less oxygen than normal Hb so erythrocytes cannot carry their function properly and they are deformed in such a way that they stick together and form clumps (impairs the blood flow and can even lead to a stroke)

Question 31

Connection between Hb genotype and malaria

Answer 31

Hb^n Hb^n genotype is healthy but, if infected, suffers badly from malaria, Hb^s Hb^s cannot be infected by malaria as plasmodium can only survive in healthy erythrocytes but it suffers badly from anemia, and the Hb^s Hb^n genotype suffers mild anemia and is protected from malaria (plasmodium cannot survive in their blood due to some chemical imbalances

Question 32

What number of nucleotides is best to be inserted or deleted as to cause the least consequences to the nucleic strand?

Answer 32

three or a multiple of three – only one a-a gets added or removed – if any other number gets inserted/deleted the entire reading frame gets changed that is all a-a are different (frameshift mutation)

Question 33

Examples of positive mutations

Answer 33

development of lighter skin (less melanin needed to protect the skin from light) in places with less sun enables greater absorption of UV light which turns previtamin D into vitamin D – lactase production in adults (should be limited only to babies)

Question 34

Gene knockout, and an example

Answer 34

the latest technique to study the function of unknown genes – organisms with dysfunctional variations of a gene of interest are made and the change in the phenotype reveals the gene’s function – e.g. p53 (higher tumor incidence and age faster)

Question 35

CRISPR (Cluster Regularly Interspaced Palindromic Repeats)

Answer 35

new gene editing technology based on the prokaryotic immune system that helps them evade viral infection – they remember (molecular memory) an old phage infection by taking a part of its DNA (spacer) each time – different spacers are separated by repeats and once a virus infects the organism a specific spacer and its repeat get transcribed to form gRNA (guide RNA) which cuts the viral DNA in order to deactivate it – CRISPR enables us to insert/delete sections of the DNA into cells with extreme precision

Question 36

Particulate inheritance

Answer 36

traits are determined by genes that separate during meiosis and reunite upon fertilization – they don’t lose their integrity but may be overshadowed by the intensity of another gene (dominant and recessive genes)

Question 37

The seven alternative phenotypic traits in pea plant

Answer 37

flower color and position, seed color and shape, pod color and shape, and height

Question 38

Phenotype vs genotype

Answer 38

set of all expressed traits (characteristics) determined by the genotype – alleles possessed by an organism (genetic potential regarding a certain trait)

Question 39

Polygenic vs monogenetic trait
alternative vs multiple alleles
homozygous vs heterozygous

Answer 39

trait determined by multiple genes – trait determined by a singular gene
only two alleles (dominant or recessive) or more than two (e.g. erythrocyte blood group)
has only one allele (no hidden) – has two different alleles

Question 40

Filial generation, what are we using to examine it?

Answer 40

the first generation whose genotype and phenotype we’re following – punnett grid is used to look at their offspring’s genotypic and phenotypic ratios